I bet it's not as effective as an old lady with 5 decades of piano teaching experience. Every town has one.
Although I'm not totally disagreeing, I think a lot depends on the student/teacher relationship. Growing up I had piano lessons and the two people teaching me (not at the same time) were very nice/patient/encouraging, however they never really grabbed my attention the way goofing off and playing with the different piano voices, and following along with my pianos built in"tutor" songs did. I think my earlier more trad…
Or, so I thought. A couple of years after I stopped formal lessons, I started composing on keyboard, and was deeply shocked to discover that when I was doing my own thing, I had no problem whatsoever playing in the key of my choice. It turns out that if you play enough scales for a given key, you can play in that key just fine.
Nevertheless I never did develop the ability to play sheet music in arbitrary keys without a lot of work constantly going into remembering the key.
I would have done a lot better with a teacher that figured out the Suzuki method was a poor match for me. Or if I had had enough knowledge to figure that out myself.